The present invention relates to a sensing system used to monitor the structural health of structures such as polymeric matrix composite structures, and more particularly, to a sensor which utilizes a conductive ink incorporating carbon nanofibers which may be applied to a structure.
Monitoring the structural health of structures which are used over long periods of time has become increasingly important. Over time, structures such as architectural and vehicular structures as well as aircraft, turbine blades, bridges, satellites, and ships can suffer from defects such as fractures and fatigue cracks. Such defects, if undetected, may result in dangerous accidents. Currently, the monitoring of such structures is time consuming and expensive. This is particularly evident where the structures to be monitored must be disassembled and transported to testing facilities. Detecting hidden defects without disassembly of the structures is even more difficult when the structures cannot be disassembled, for example, in the case of buildings and bridges.
Conventional strain gages are known in the art but are not appropriate for monitoring the structural health of large structures as they cover a relatively small sensing area of up to several inches and require sophisticated calibration and electronics to monitor the strain. A more recent monitoring approach has been the development of a strain sensor which uses conductive particles dispersed in a polymer. This strain sensor has shown significant promise for monitoring gross deformation in civil structures. See, for example, U.S. Pat. No. 6,276,214. However, in use, the sensor must be adhered to a film which is then adhesively bonded to a structure. Such a system requires a durable adhesive in order to ensure that the sensor does not peel off over time. In addition, such a sensor may be difficult to apply to rough or uneven surfaces.
Accordingly, there is a need in the art for a sensor which can quickly and easily monitor the structural health of structures such as composite structures, which can be applied to complex contours, and which is environmentally durable.